I really don't see the point of using cars (parts are fine). You should build your own. It's a lot easier than you think and you get full understand and control of your vehicle. Learning and mastering someone else's vehicle usually takes longer and it may not solve your specific transportation needs all the time.
Besides it being flat-out wrong that mastering a framework takes longer than building one (you will have to support it), the typical framework is a lot larger than the code of the applications built on top of them.
Building a framework is a bit like writing a DSL, a good framework abstracts out the work that would otherwise be duplicated many times over and will help to standardise the codebases of various projects and will help to allow integration of bits and pieces from different projects in a re-usable way.
There is a reason why rails, django, drupal and a bunch of others are wildly popular, they save people oodles of time.
Both the framework and no framework approaches have merit.
Choosing a framework limits your choices. If I'm using Django, it won't work (or work well) with a non-rel backend. If I'm using jQuery and I need to update one of the libraries (say jQuery UI) I might have to update jQuery as well, etc.
What you think saves oodles of times doesn't always. The odd bug, the odd crash etc that keeps popping up may have roots in the framework that you chose and that you're using without having knowledge of its internals. The framework might make your app much slower and cost you in terms of hardware.
Not using a framework is harder work initially, but with the right libraries it isn't that big of a leap. Picking up a smaller framework with libraries can be a surprisingly easy and a lot more flexible when your needs end up being different from what the framework intended.
Ofcourse, there is a flip side to it all and I understand your point :) Micro-frameworks are the best IMO, not the beasts that Rails/Django are.
